1. Field of the Invention
This invention relates to the field of expansion joints for abutting slabs or panels wherein the joint is to be covered by a facing or covering material. In particular, the invention concerns an expansion joint between abutting decks in a building, to be covered with a facing material such as carpeting, tile or other coverings arranged to bear traffic. The invention also relates to expansion joints in walls, ceilings, etc., wherein a facing material is to be placed smoothly over a varying gap between abutting panels.
2. Prior Art
An expansion joint in a floor, wall, ceiling or other structure joins two members defining substantially coplanar surfaces on at least one side, the two members generally abutting along a line but defining a gap between them that varies in width over time. The width of the gap can change as a function of temperature and load variations on the means supporting the two members. To avoid cracking and similar structural failure of the two members or the means supporting them, the expansion joint allows the joint to vary in a flexible manner.
Known expansion joints have a number of objectives relating to maintaining a connection between the two relatively movable members notwithstanding the gap, and/or maintaining a smooth surface over the gap, for example for bearing traffic, and sealing between the two members. It is usually desirable that the joint not define a discontinuity in the surface defined by the abutting slabs, panels or the like. In a floor expansion joint for example, a discontinuity on an upper surface is a tripping hazard. Where a joint on a floor, wall, ceiling or the like is to be covered for example by carpeting, wall coverings, etc., a discontinuity may form in the covering material. This problem is not resolved even if the expansion joint itself maintains a smooth upper surface for the joined members The discontinuity of course varies with the gap between the abutting members.
If one attempts to merely cover over an expansion joint, problems arise from the need to maintain an even upper surface and thereby avoid a tripping hazard. For example, it is possible to attach a flat strip of metal or other stock to cover the gap in an expansion joint. The strip is attached to one of the panels and allowed to extend across the gap to lap over the other panel by an amount greater than a span of variation in the width of the gap. To avoid raised edges, settable floor compound can be applied adjacent the strip and feathered (made progressively thinner) proceeding away from the strip to form a very gradual hump up to the level of the thickness of the strip. Such feathered floor compound is effective to avoid a tripping hazard on the side of the joint where the strip is attached to one of the panels. On the other side, however, expansion causes a gap to open between the extreme edge of the strip and the edge of the flooring compound. Contraction of the joint exerts a pressure between the strip and the flooring compound tending to break away the flooring compound or causing the strip to bow upwardly. In any of these cases, this technique is not effective to obtain a smooth upper surface without a tripping hazard in at least some of the conditions of the expansion and/or contraction of the gap.
The abutting members of an expansion joint are generally relatively movable laterally toward and away from the gap, but also may be movable longitudinally along the gap. Both forms of relative movement present the possibility of a bulge, ripple or similar discontinuity in any covering material. Assuming that it is possible to provide an expansion joint with variable length connecting structures that maintain a smooth upper surface, such structures still do not solve problems associated with covering layers, particularly of flexible material, applied over the gap. A carpet applied over a gap, for example, will bulge when the gap closes and will stretch or pull away from its moorings when the gap opens, even if the expansion joint applied to the floor is fully effective to maintain a smooth upper surface of the joined members. There is a need to resolve the problems associated with expansion joints where the joint is to be covered.
In known expansion joint structures, connection flanges forming the opposite sides of the joint across the gap are rigidly fixed to the edges of the two members to be joined across the gap, and flexible or length-variable elements of the joint bridge across these rigidly-fixed flanges. The flanges are arranged flush with the surfaces of the two members, typically on the upper surface and also on the surface facing the gap. This requires that a space be formed in the two members for receiving the joint flanges such that the joint flanges are flush with the top surface and the end faces of the joined members. U.S. Pat. No. 3,372,521--Thom discloses a floor joint cover assembly wherein bolts are embedded in both members of a floor joint formed of cast slabs, and the upper edges of the members at the end faces adjacent the joint are contoured to a shape complementary with the joint flanges. The structure must be installed when the slabs are not yet hardened, such that the bolts can be embedded and the complementary shape formed. It is possible in a joint of this type to mill out the area of the slabs to be occupied by the joint flanges after the slabs are set, or to devise molding frames of a shape complementary with the joint flanges, such that the necessary shape is obtained when poured slabs set. However, both these alternatives are complex and expensive. Moreover, the resulting joints do not resolve the problems of flexible coverings such as carpets.
U.S. Pat. No. 3,390,501--Driggers (see FIG. 2) discloses a joint having a structure that protrudes upwardly from the joint in the area of the gap, by an amount equal to the height of finish materials such as plasterboard, which finish material abuts the protruding portions of the joint at both sides. This is an alternative to a joint similar to that of Thom, wherein anchoring structures must be embedded in a wet or green slab. The joint may be useful where the facing material (e.g., plasterboard) on the slab on either side of the joint is rigidly connected to the slab, and in view of the rigid structures of the slab and facing material, the composite structure is similar to that of Thom in that the joint resides flush in a complementary contour formed at the facing edges of the two rigid composite joined members. Notwithstanding these aspects, the Driggers joint defines a surface discontinuity and a resulting tripping hazard if the joint is used for floors.
One method of minimizing problems with gapping at an expansion joint is to provide a cover panel that floats between the end faces of the joined members, and means for centering the floating cover panel. An example is disclosed in U.S. Pat. No. 3,745,726--Thom. This means for dealing with the gap effectively reduces the extent of gap by splitting the gap in half, i.e., producing a smaller gap at each side of the floating panel rather than one full width gap. Nevertheless, gap problems remain.
Other joint structures having joint flanges embedded in the material of the slabs or the like are shown in U.S. Pat. Nos. 4,774,795--Braun; 4,784,516--Cox; and, 4,833,851--Ohmatsu. In general, the joints have flanges rigidly attached to the joined slab members, which flanges define a nip area between them over at least a portion of their extension, that encloses a flexible material. If the gap opens or closes, either a bulge will be raised in the flexible material or a gap will open at an edge. Therefore, these joints lack a continuous smooth coverage across the surface of the joint. If the joints are covered by a finish material (rather than simply provided with a finish material reaching just to the respective edges), the finish material will bulge or stretch even if the joint remains smooth.
U.S. Pat. No. 4,111,582--Tippett discloses a flexible material in a nip that is covered over by a continuous covering layer. Assuming that the flexible material is precisely dimensioned and has the necessary range of expansion without bulging, the joint does not arrange for expansion and contraction movements in the covering material. Instead, the slab members are arranged to move relative to the covering material and the covering material is fixed in place by undisclosed means.
There has been a need to simplify expansion joints while ensuring that the joint maintains a smooth upper surface. The complex expansion joints of the foregoing patents are quite expensive in terms of materials. As a result of the need for embedding the joint flanges in the edges of the joined members, such expansion joints are even more expensive to install. The present invention employs a joint member that is an integral body and attaches to only one of the two joined members. The joint member is easily and inexpensively surface mounted. The joint member overlaps the surface covering material by a fixed amount on the attached-side slab or the like, and overlaps by a variable amount on the opposite side, thereby accommodating expansion and contraction. In the central area of the joint member bridging across the joined members, the joint member is also provided with a strip of facing material, tending to better conceal the joint by providing a relatively uninterrupted extension of facing material across the joint. The joint is effective, and accommodates flexible facing material, at a fraction of the cost of other expansion joints in either materials or installation.